Gas turbine engine with variable area fan nozzle positioned for starting

ABSTRACT

A gas turbine engine has a compressor section, a low spool, and a fan. The fan delivers air into the compressor section and into a bypass duct having a variable area nozzle. The compressor section compresses air and delivers it into a combustion section. The combustion section mixes air with fuel, igniting the fuel, and driving the products of the combustion across a turbine. The turbine drives the low spool. A control for the gas turbine engine is programmed to position the nozzle at startup of the engine to increase airflow across the fan. A variable inlet guide vane is positioned upstream of the compressor section. The control also positions the variable inlet guide vane at start-up to increase air flow across the compressor section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/367,579, filed Feb. 7, 2012, now U.S. Pat. No. 8,291,690, whichclaims priority to U.S. Provisional Application No. 61/592,672, whichwas filed Jan. 31, 2012.

BACKGROUND

This application relates to a gas turbine engine having an inlet guidevane which has its position controlled to increase windmilling speed ofengine components.

Gas turbine engines are known, and typically include a fan deliveringair into a bypass duct outwardly of a core engine, and into a compressorin the core engine. Air in the compressor is passed downstream into acombustor section where it is mixed with fuel and ignited. Products ofthis combustion pass downstream over turbine rotors, driving them, andin turn drive the compressor and fan. Recently it has been proposed toinclude a gear reduction between a low pressure compressor and the fan,such a low pressure turbine can drive the two at distinct speeds.

A gas turbine engine as used on an aircraft must be able to start underseveral conditions. First, the gas turbine engine must be able to startwhen on the ground. A starter can be used on the ground. Second, the gasturbine engine must be able to start in the air. In the air, at lowerspeeds of the aircraft, the normal starter for the gas turbine enginemay be utilized to begin driving the turbine/compressor rotors. However,at higher speeds the starter may not be utilized. At higher speeds socalled “windmilling” is relied upon at startup. Windmilling typicallyoccurs as the compressor and fan rotors are driven by the air beingforced into the core engine, and the bypass duct, as the aircraftcontinues to move.

SUMMARY

In a featured embodiment, a gas turbine engine has a compressor section,a low spool, and a fan. The fan delivers air into the compressor sectionand into a bypass duct having a variable area nozzle. The compressorsection compresses air and delivers it into a combustion section. Thecombustion section mixes air with fuel, igniting the fuel, and drivingthe products of the combustion across a turbine. The turbine drives thelow spool. A control for the gas turbine engine is programmed toposition the nozzle at startup of the engine to increase airflow acrossthe fan. A variable inlet guide vane is positioned upstream of thecompressor section. The control also positions the variable inlet guidevane at start-up to increase air flow across the compressor section.

In another embodiment according to the foregoing embodiment, thecompressor section includes a high pressure compressor and a lowpressure compressor. The turbine includes a low turbine driving the lowspool and the low pressure compressor.

In another embodiment according to any of the foregoing embodiments, thefan is driven with the low pressure compressor by the low spool. Thereis a gear reduction between the fan and the low spool.

In another embodiment according to any of the foregoing embodiments, thecontrol includes stored desired positions for the nozzle to provideincreased airflow into the compressor at startup at various conditions.

In another embodiment according to any of the foregoing embodiments, thevarious conditions include the altitude of an aircraft carrying the gasturbine engine, and an air speed of the aircraft.

In another embodiment according to any of the foregoing embodiments, theconditions also include a speed of the low spool when startup isoccurring.

In another embodiment according to any of the foregoing embodiments, theposition of the nozzle is selected to increase airflow across the fanwhile an aircraft associated with the gas turbine engine is in the air,and to increase windmilling speed of the turbine.

In another embodiment according to any of the foregoing embodiments, thenozzle is moved toward a full open position to increase windmillingspeed.

In another embodiment according to any of the foregoing embodiments, thepositioning of the variable inlet guide increases air flow across thelow pressure compressor.

In another embodiment according to any of the foregoing embodiments, thecontrol includes stored desired positions for the nozzle to provideincreased airflow into the compressor section at startup at variousconditions.

In another embodiment according to any of the foregoing embodiments, thevarious conditions include the altitude of an aircraft carrying the gasturbine engine, and an air speed of the aircraft.

In another embodiment according to any of the foregoing embodiments, theconditions also include a speed of the low spool when startup isoccurring.

In another embodiment according to any of the foregoing embodiments, theposition of the nozzle is selected to increase airflow across the fanwhile an aircraft associated with the gas turbine engine is in the air,and to increase windmilling speed of the turbine.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a gas turbine engine.

FIG. 2 is a schematic of a control logic circuit.

FIG. 3 is a flowchart.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath B whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 to drive the fan 42 at a lower speed than the lowspeed spool 30. The high speed spool 32 includes an outer shaft 50 thatinterconnects a high pressure compressor 52 and high pressure turbine54. A combustor 56 is arranged between the high pressure compressor 52and the high pressure turbine 54. A mid-turbine frame 57 of the enginestatic structure 36 is arranged generally between the high pressureturbine 54 and the low pressure turbine 46. The mid-turbine frame 57further supports bearing systems 38 in the turbine section 28. The innershaft 40 and the outer shaft 50 are concentric and rotate via bearingsystems 38 about the engine central longitudinal axis A which iscollinear with their longitudinal axes.

The core airflow C is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle.The geared architecture 48 may be an epicycle gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.5:1. It should be understood, however, that theabove parameters are only exemplary of one embodiment of a gearedarchitecture engine and that the present invention is applicable toother gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of 1 bm of fuel being burned divided by 1 bf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tambient degR)/518.7)^0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

The gas turbine engine 20 is provided with controls and features tooptimize starting.

A starter 400 (shown schematically) is typically included with a gasturbine engine, and is relied upon to begin driving the high spool whenthe engine is started. This will typically occur when the airplane is onthe ground, and is a relatively simple process at that time.

On the other hand, there are times when the gas turbine engine is shutdown while an aircraft associated with the gas turbine engine is stillin the air. At lower air speeds, the starter may be utilized while theaircraft is in the air to begin driving rotation of the spool 32 tobegin the restart process. Of course, once the combustion section hasbegun to ignite and burn the fuel, then the products of combustion willtake over driving the turbine rotors and the starter may stop.

Under certain conditions, use of the starter while the aircraft is inthe air is not advised or is not possible. Under those conditions, theforce of air being driven into the engine core, and across the fan 42 isrelied upon to drive the turbine rotors, and the compressor rotors. Thisprocess is called “windmilling.”

It is desirable to increase the speed of windmilling of the high spoolthat occurs when it is necessary to restart the engine because higherwindmill speeds drive higher airflow.

The engine is provided with equipment that is controlled to optimize toincrease the ability to maximize windmilling of the high spool. Thus, anactuator 180 selectively drives a control to position a compressor inletguide vane 184 which is just forward of the forward most low compressorrotor 186.

An angle of the vane 184 is preferably positioned to maximize the flowof air reaching the rotor 186 while the aircraft is being restarted. Inflight, this would be positioning the vane 184 such that the air beingforced into the core engine as the aircraft continues to move throughthe air with engine 20 not being powered, is maximized.

Also, the bypass airflow B may be maximized by positioning a variablefan nozzle 200. The variable fan nozzle 200 is controlled by an actuator204, shown schematically, to move axially and control the flow area at202. Generally, one would open the nozzle to a full open position tomaximize this air flow.

Both the inlet guide vane 180 and the actuator 204 for the variable areafan nozzle 200 are generally as known. However, they have not beenutilized at startup to maximize the amount of windmilling which occurs.

In general, it is desirable to position the vane 184 to maximize airflowthrough the core engine, and position the variable area nozzle 200 tomaximize airflow across the fan 42. Airflow across the fan 42 will drivethe fan to rotate, and air being forced into the core engine will causethe compressor rotor 186 to rotate.

Applicant has developed a control system as shown in FIG. 2 which takesin altitude signals 210, an aircraft speed signal 212, and a signal 214which is the windmilling speed of the low spool 30.

Lookup tables are stored in control component 216, 218 and 222.Applicant has developed tables which associates particular altitudesengine speed, or Mach number, with a desired position for the vane 184,and/or the position of the nozzle 200 to maximize the airflow asdiscussed above. The desired positions can be developed experimentallyand will vary by aircraft and engine design. While the two features maybe used in combination, it is also within the scope of this applicationthat each could be used individually without the other, whereappropriate.

The control of the variable inlet guide van is disclosed in co-pendingapplication entitled Gas Turbine Engine With Compressor Inlet Guide VanePositioned for Starting, filed on even date herewith, Ser. No.13/367,742.

The signal passes downstream to a block 224, wherein additional signalscome from control elements 218 and 216. Element 218 and 216 provide anadjustment to the output of element 222 based upon the low spool 30speed altitude and aircraft airspeed.

Downstream of the block 224, a signal passes to the actuators 180 and/or204. The FIG. 2 control can be incorporated into a FADEC 199.

Of course, if the aircraft is positioned on the ground, the altitudewould be generally the same, and the Mach number would be zero. Further,the low spool speed might be zero. Even so, there would be desiredpositions for the vane 184 and/or nozzle 200. If the aircraft is in theair when being restarted and moving at a relatively slow Mach number, itmay be possible to utilize a starter 400, shown schematically, incombination with the windmilling. However, this would all beincorporated into the lookup tables stored in component 216. Also, asmentioned above, at times the starter 400 cannot be relied upon in somecircumstances. Again, this would be anticipated and relied upon atcomponents 216, 218 and 222 or in the look-up table.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A gas turbine engine comprising: a compressorsection; a low spool; a fan; said fan delivering air into saidcompressor section and into a bypass duct having a variable area nozzle,and said compressor section compressing air and delivering it into acombustion section; the combustion section mixing air with fuel,igniting the fuel, and driving the products of the combustion across aturbine, said turbine driving said low spool; a control system for saidgas turbine engine, programmed to position said variable area nozzle atstartup of the engine to increase airflow across said fan; and avariable inlet guide vane is positioned upstream of said compressorsection, and said control system also positioning said variable inletguide vane at start-up to increase air flow across said compressorsection.
 2. The engine as set forth in claim 1, wherein said compressorsection includes a high pressure compressor and a low pressurecompressor, and said turbine includes a low turbine driving said lowspool and said low pressure compressor.
 3. The engine as set forth inclaim 2, wherein said fan is driven with said low pressure compressor bysaid low spool, and there being a gear reduction between said fan andsaid low spool.
 4. The engine as set forth in claim 3, wherein saidcontrol includes stored desired positions for said variable area nozzleto provide increased airflow into the compressor at startup at variousconditions.
 5. The engine as set forth in claim 4, wherein said variousconditions include the altitude of an aircraft carrying the gas turbineengine, and an air speed of the aircraft.
 6. The engine as set forth inclaim 5, wherein the conditions also include a speed of the low spoolwhen startup is occurring.
 7. The engine as set forth in claim 6,wherein the position of said variable area nozzle is selected toincrease airflow across the fan while an aircraft associated with thegas turbine engine is in the air, and to increase windmilling speed ofthe turbine.
 8. The engine as set forth in claim 7, wherein saidvariable area nozzle is moved toward a full open position to increasewindmilling speed.
 9. The engine as set forth in claim 2, wherein saidpositioning of said variable inlet guide vane increases air flow acrosssaid low pressure compressor.
 10. The engine as set forth in claim 9,wherein said various conditions include the altitude of an aircraftcarrying the gas turbine engine, and an air speed of the aircraft. 11.The engine as set forth in claim 10, wherein the position of saidvariable area nozzle is selected to increase airflow across the fanwhile an aircraft associated with the gas turbine engine is in the air,and to increase windmilling speed of the turbine.
 12. The engine as setforth in claim 1, wherein said control includes stored desired positionsfor said variable area nozzle to provide increased airflow into thecompressor section at startup at various conditions.
 13. The engine asset forth in claim 12, wherein the conditions also include a speed ofthe low spool when startup is occurring.